The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Encoding of data for a video includes an intra prediction encoding and an inter prediction encoding. The intra prediction encoding and the inter prediction encoding corresponds to an effective method which can reduce the correlation between data and is widely used for compression of various data. Especially, in the inter prediction encoding, since a motion vector of a current block determined through estimation of the motion of the current block closely relates to motion vectors of neighboring (or adjacent) blocks, it is allowed to calculate a Predicted Motion Vector (PMV) for the motion vector of the current block from the motion vectors of the neighboring blocks and then encode a Differential Motion Vector (DMV) for the PMV without encoding the value of the motion vector of the current block itself, which can considerably reduce the quantity of bits to be encoded, so as to improve the encoding efficiency.
That is, in the case of performing an inter prediction encoding, an encoder encodes and transmits a differential vector which corresponds to a differential value between a current motion vector and a predicted motion vector determined through estimation of the motion of the current block from a reference frame reconstructed through previous encoding and decoding. Also, a decoder reconstructs a current motion vector by adding a predicted motion vector and a differential vector transmitted by predicting a motion vector of a current block by using a motion vector of previously decoded motion vectors of neighboring blocks.
Further, at the time of performing an inter prediction encoding, the resolution may be collectively raised by interpolating the reference frame, and the differential vector corresponding to a differential value between the current motion vector and the predicted motion vector determined through estimation of the motion of the current block may be then encoded and transmitted. In this event, an increase in the resolution of the reference frame enables a more exact inter prediction, thereby reducing the quantity of bits generated by the encoding of a residual signal between an original image and a predicted image. However, such an increase of the resolution of the reference frame may also increase the resolution of the motion vector, which increases the quantity of bits generated by the encoding of the differential vector. In contrast, a decrease in the resolution of the reference frame increases the quantity of bits generated by the encoding of a residual signal but decreases the resolution of the motion vector, which thereby decreases the quantity of bits generated by the encoding of the differential vector.
The inventor(s) has noted that in the inter prediction encoding according to the prior art, all blocks, slices, and pictures of an image, which correspond to encoding units of the image, are interpolated with the same resolution, and an inter prediction encoding is then performed using a motion vector of the same resolution for all of them. For example, in the case of H.264/AVC standard, the resolution of the motion vector is fixed to a ¼ resolution. The inventor(s) has experienced that an increase of the motion vector causes an increase of the residual signal to thereby degrade the compression efficiency.
Further, the inventor(s) has experienced that since the inter prediction decoding corresponds to the inter prediction encoding, the degradation of the compression efficiency in the inter prediction encoding makes it difficult to expect a high efficiency of the inter prediction decoding.